Very nice explanation. I have one question, if you are taking R group as a iPr, then enolisation occur from other side because, NEt3 is not that much strong and bulky base.
The main idea is there has to be a difference between the two sides of the carbonyl do differentiate between. The NEt3 is bulky enough but not too bulky to be able to get the H off the ethyl group but not the isopropyl group just on sterics. This is the dominant thing going on. I’m going to touch on this in my next video: another factor is the isopropyl group’s bulk favours the boron Lewis acid sitting on the ethyl group side. There’s also a Stereoelectronic effect that helps make the ethyl group’s protons a bit more acidic. These reactions are done at low temperatures when you need to be careful to select so small differences in activation energies are enough to get selectivity.
Many thanks :). I'll probably do some extension material on this type of aldol topic in the future as there's all sorts of ways of building stereocontrol into these models.
Hlw casual chemistry I love your lecture series. It helps me a lot even at my master's degree. I have a small question in your retrosynthesis series you said that boron enolisation give Z enolate but here E enolate gets formed. Here bulky iso propyl also present.
That's great to hear - glad the videos are useful :) I think I've understood which other video your question refers to With the boron-mediated enolisation, it is very dependent on what you choose as the substituents/ligands on the boron centre and what you choose as the base. Hence, this technique is a reagent-controlled enolisation. Although others options exist, two common reliable techniques are: (1) For making Z enolates - use Bu2BOTf and iPrEt2N. This is a small alkyl substituent, a really good leaving group in the triflate, and a slightly bulkier base. (2) For making E enolates - use Cy2BCl and Et3N. This is a bulkier alkyl substituent, a less good leaving group in the chloride, and a slightly smaller base. I should probably get around to making a video lecture of some sort on enolates as I have lots of teaching materials on this topic as it's very close to my PhD work.
Where were your videos during my undergrad? 😂 Good content, keep it up!
Thanks for the feedback and glad you enjoyed the video 🙂
Very nice explanation. I have one question, if you are taking R group as a iPr, then enolisation occur from other side because, NEt3 is not that much strong and bulky base.
The main idea is there has to be a difference between the two sides of the carbonyl do differentiate between. The NEt3 is bulky enough but not too bulky to be able to get the H off the ethyl group but not the isopropyl group just on sterics. This is the dominant thing going on.
I’m going to touch on this in my next video: another factor is the isopropyl group’s bulk favours the boron Lewis acid sitting on the ethyl group side. There’s also a Stereoelectronic effect that helps make the ethyl group’s protons a bit more acidic.
These reactions are done at low temperatures when you need to be careful to select so small differences in activation energies are enough to get selectivity.
Thanks for your wonderful explanation.
🙂 Glad you enjoyed the video
Very good😊 when I understand problem I bacome very happy
🙂
Great explanation.
Many thanks :). I'll probably do some extension material on this type of aldol topic in the future as there's all sorts of ways of building stereocontrol into these models.
@@CasualChemistry Yes, that would be very great for everyone. Please.
Hlw casual chemistry I love your lecture series. It helps me a lot even at my master's degree. I have a small question in your retrosynthesis series you said that boron enolisation give Z enolate but here E enolate gets formed. Here bulky iso propyl also present.
That's great to hear - glad the videos are useful :) I think I've understood which other video your question refers to
With the boron-mediated enolisation, it is very dependent on what you choose as the substituents/ligands on the boron centre and what you choose as the base. Hence, this technique is a reagent-controlled enolisation. Although others options exist, two common reliable techniques are:
(1) For making Z enolates - use Bu2BOTf and iPrEt2N. This is a small alkyl substituent, a really good leaving group in the triflate, and a slightly bulkier base.
(2) For making E enolates - use Cy2BCl and Et3N. This is a bulkier alkyl substituent, a less good leaving group in the chloride, and a slightly smaller base.
I should probably get around to making a video lecture of some sort on enolates as I have lots of teaching materials on this topic as it's very close to my PhD work.
@@CasualChemistry that will be great and thank you once again